The present invention relates generally to mechanisms for attaching printed circuit boards to support structures in electronic apparatus. More particularly, the invention relates to an attachment mechanism particularly, but not exclusively, suitable for securely coupling a computer""s motherboard to its casing or chassis.
In modern personal computer systems, the motherboard is attached to a casing that houses various internal components of the computer. The motherboard typically supports most of the integrated circuits that are included in the computer system. Generally, the motherboard will also include connectors adapted to receive expansion boards as well as to receive expansion memory.
It is important to firmly secure the motherboard within the computer casing so that vibrations caused, for instance, by the computer""s ventilation fans or shocks to the computer do not cause expansion boards or memory modules to come loose or other components to be loosened or their connections damaged.
In the prior art, there are a wide variety of different mechanisms that have been used and proposed to secure the motherboard to the chassis. Examples of such arrangements can be found in U.S. Pat. Nos. 5,434,746 and 4,901,205. In practice, however many computer motherboards are simply screwed to the chassis.
U.S. Pat. No. 5,214,569 describes one arrangement in which a plurality of keyhole shaped fitting holes are formed in the motherboard. The holes are adapted to fit over posts extending from the chassis through enlarged opening portions of the holes. The motherboard is then slid over the posts such that the post shafts slide into slot portions of the holes with a head portion of the posts being arranged to fit tightly over the top surface of the motherboard.
In this way, the motherboard can be firmly anchored to the chassis, yet simply and easily removed without the use of tools.
However, since the casing of a personal computer also serves as an electromagnetic shield, a computer motherboard also needs reliable electrical connections to the chassis at a number of different points in order to ground the casing. It is important that these connections are also able to survive the various shocks and vibrations to which the computer may be exposed since the loss of one or more of these connections may modify the EMI performance of the apparatus as a whole. Where the motherboard is screwed to the chassis, these connections are usually provided by the motherboard mounting screws.
This invention is directed to providing a mounting arrangement for a computer motherboard that provides both a reliable mechanical and a reliable electrical connection between the motherboard and a support structure.
In brief, this is achieved by electronic apparatus comprising a printed circuit board mounted on a support structure, the printed circuit board having at least one keyhole shaped fixing hole, the support structure being provided with at least one electrically conducting fixing post having an at least partially circumferential slot for engaging the fixing hole, wherein the printed circuit board has a conducting surface adjacent said fixing hole that is disposed to provide an electrical contact with said post so as to establish an electrical circuit between at least one component mounted on the printed circuit board and the support structure.
This provides a convenient mounting mechanism which allows the motherboard to be securely mounted on the support structure and to provide an electrical connection thereto.
Preferably the apparatus comprises a resilient washer for engaging the slot. The washer can be electrically conducting and positioned in the slot so as to engage the conducting surface on the printed circuit board.
In one implementation, the fixing post is an integrally formed metallic item and comprises screw-threaded means for mounting said posts on the support structure. This allows the board to be fixed into the screw-threaded holes that are standardly provided on a personal computer chassis.
One advantage of this arrangement is that the motherboard is not present at the time fixing posts are screwed to the chassis, the motherboard being subsequently clipped to the posts. This avoids the risk of damage to the motherboard through slipping of the screwdriver used to mount it. The screwdriver used to mount prior art screw mounted motherboards has been found in practice to be a common source of damage to the motherboards.